In a bowl, combine the ground beef, salt and pepper until just combined. Allow the ground beef to sit at room temperature for 15 minutes, then form it into 4 equal sized patties. Heat a large skillet over medium-high heat and add the olive oil and butter. Add the burgers and cook until your desired doneness – for medium-well, I do about 5 minutes per side. After you flip the burgers once, cover the tops with the slices cheddar cheese. At this point I like to cover the skillet and allow the cheese to melt all around the burger. You can also grill the burgers, obviously.